The invention concerns a power distribution transmission.
Power distribution transmissions, especially as continuously variable transmissions, are often used to drive motor vehicles, particularly field tractors. Especially adequate here are power distribution transmissions having a mechanical power branch and a hydraulic power branch consisting of a hydraulic pump and a hydraulic motor, preferably with a pump of adjustable displacement. Since during operation of the power distribution transmission, mainly the hydraulic power branch produces strong vibrations which in case of fixed connection of the hydraulic motor and the hydraulic pump with the transmission housing pass on the vibrations to the transmission housing causing loud noise, the hydraulic pump and the hydraulic motor have to be uncoupled from the transmission housing.
DE 44 01 509 A1 discloses a continuously variable transmission with power distribution, especially for motor vehicles, which consists of a hydraulic power branch and a mechanical power branch, there being interconnected in the hydraulic power branch a hydraulic pump and a hydraulic motor and in order to uncouple the hydraulic motor and the hydraulic pump from the housing, they are retained in the transmission housing by damping elements. Damping elements are mounted respectively on each side of the hydraulic motor-pump unit through which the forces in the transmission housing can be transmitted. The suspension is configured so as to create a three-point support which is mounted respectively on the input and output side of the continuously variable converter, consisting of the hydraulic pump and the hydraulic motor, as central bearing for fixing the position of the central axle of the continuously variable converter in relation to the transmission housing and a third bearing as supporting bearing for torque support and optionally axial support of the continuously variable converter and that the central bearing is designed so as to make possible a rotation of the continuously variable converter around its central axle against the torque-supporting bearing. In order to make possible mounting in the transmission housing, the hydraulic motor and the hydraulic transmission with the damping devices, the transmission has to have a divided housing in order to make possible the installation of the hydraulic motor and the hydraulic pump in the transmission housing. If manufacturing tolerances appear, it is possible with this arrangement that the hydraulic motor and the hydraulic pump is installed transversely in the transmission housing whereby, during operation of the power distribution transmission, the damping elements are already compressed to their initial position with the result that the damping of noise is considerably limited. In the transmission, since the input wheels for driving the hydraulic pump and the output wheels on the hydraulic motor are fixedly connected with the shafts of the hydraulic pump and of the hydraulic motor, vibrations and therewith movements are directly transmitted to the running gears in the mechanical power branch whereby the engagement geometry of the running gears is constantly altered.
The problem on which this invention is based is to provide a power distribution transmission having a hydraulic and a mechanical power branch in which the vibrations of the hydraulic power branch are only dampedly emitted to the parts surrounding the hydraulic power branch and the hydraulic power branch stands out by easy installation in the transmission housing.
According to the invention, the hydraulic power branch consists of a hydraulic pump and a hydraulic motor which are interconnected and in the area of the connection of the hydraulic motor and the hydraulic pump are connected via damping elements with the transmission housing. The hydraulic motor and the hydraulic pump are preferably interconnected via an intermediate plate, which radially to the axis of rotation of the hydraulic pump, has receptacles for the damping elements by which the intermediate plate can be connected with the transmission housing. But it is also possible to situate the damping elements in receptacles of the transmission housing and connect them with the intermediate plate. The intermediate plate can also be designed integrally with the housing of the hydraulic motor or the housing of the hydraulic pump. While the hydraulic pump and the hydraulic motor, dampened on their connecting point with the damping elements located in one plane, are supported in the transmission housing, the hydraulic pump-motor unit is retained in the area of its center of gravity and can move in all three axle planes against the elasticity of the damping elements. A separation of the transmission housing is not required, since the intermediate plate can be installed in the transmission housing from one side of the pump-motor unit via fastening elements, preferable a screw connection. The pump-motor unit thus has to be fastened only in its half of the transmission housing. The transmission housing preferably has receptacles for centering pins with which, during the installation, the hydraulic pump and the hydraulic motor are centered in the transmission housing and then connected with the transmission housing by the damping elements. After the hydraulic pump and the hydraulic motor have been fastened in the transmission housing by the damping elements, the centering pins can be removed again. Hereby is ensured a simple installation where, even in the presence of manufacturing tolerances, the hydraulic pump and the hydraulic motor can be installed in the position in which the hydraulic motor-pump unit achieves the required installation position. Input and output shafts of the hydraulic pump and of the hydraulic motor are connected via shafts with the toothed wheels which are in communication with the mechanical power branch, and are supported floatingly, on one side, in the shafts of the hydraulic pump or of the hydraulic motor and, on the other side, in toothed wheels connected with the mechanical power branch. The shafts each have, on their connections with the toothed wheels and the hydraulic pump or the hydraulic motor, crowned teeth or engaging gears designed as spiral gearing with which can be compensated, in combination with the floating support of the shaft, skewed positions or movements of the hydraulic pump and of the hydraulic motor. The toothed wheels, which accommodate the shaft for connection with the hydraulic motor or the hydraulic pump, are supported in the transmission housing so that movements of the hydraulic pump or of the hydraulic motor cannot be transmitted to the running gears of the toothed wheels. It is hereby ensured that the running gears always have the same engagement geometry during operation. Since crowned teeth or a spiral gearing have a smaller contact surface than a straight toothing, the bone conduction is transmitted to a lesser extent than in a standard toothed shaft connection. The hydraulic power branch is thus, on one hand, supported with dampened vibration in the transmission housing in one plane, via the damping elements in the center of gravity of the hydraulic motor whereby an optimal degree of freedom and an easy installation are obtained and, on the other, connected via shafts having crowned teeth with the mechanical power branch whereby the bone conduction is also reduced.